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Full list of author information is available at the end of the articleBackground Ankylosing spondylitis (AS) is the representative rheum-atic disease of seronegative spondyloarthropathy and is characterized primarily by recurrent inflammatory back pain and bilateral sacroiliitis [1]. Hip ankylosis, which is typically accompanied by enthesis heterotopic ossification (HO), occurs in about one-third of patients suffering from AS [2]. Entheopathy in peripheral and axial sites induces distinct pathologic changes, and inflammatory enthesitis is clinically detectable in approximately 10 % of patients suf-fering from early-stage AS and 50 % of those suffering from established AS [3]. Fibroblasts are the most numer-ous connective tissue cells in enthesis or ligament tissue (LT) and are reported to be associated with heterotopic ossification (HO) in LT [4,5]. However, the relevant mech-anism by which fibroblasts mediate HO remains unclear. * Correspondence